1. Technical Field
Embodiments of the present invention relate to an electronic device and a method for manufacturing thereof, and more particularly to a structure and a manufacturing process of an electronic device having a functional element such as a micro electromechanical system (MEMS) disposed in a cavity portion formed on a substrate.
2. Related Art
Electronic devices that include a functional element such as a MEMS disposed in a cavity portion formed on a substrate, are generally known. For example, a MEMS such as a micro resonator, a micro sensor or a micro actuator is housed in a cavity portion in an operable state because the micro structure needs to be disposed in a state that permits vibration, deformation and such other operations.
JP-A-2005-297180 and JP-A-2005-123561 are examples of related art.
As a way to form the cavity described above, a method disclosed in JP-A-2005-297180 is known, in which a micro mechanical element is formed on a surface of one substrate, the one substrate being then joined in a vacuum chamber with another substrate, with an O ring therebetween, and subsequently a sealant material is filled outside the O ring.
A method disclosed in JP-A-2005-123561 is also known as another way to form the cavity. In the method, a MEMS structure is formed on a substrate, and then a sacrificial layer is formed thereon. A first sealant member having through holes is further formed on the sacrificial layer, and the sacrificial layer is subsequently removed through the through holes of the first sealant member to release the movable part of the MEMS structure. Finally, the through holes of the first sealant member are closed by being covered with a second sealant member such as a chemical vapor deposition (CVD) film.
However, one of the problems of the first method described above, in which two substrates are joined, is that it increases the material cost because it requires another substrate to be used exclusively for the sealing. In addition, even though the use of an ordinary semiconductor manufacturing technique is desired, the special process of joining the two substrates, which the method requires, diminishes the merit of using the semiconductor manufacturing technique, increasing the manufacturing cost.
Furthermore, the second related art document described above, which proposes the above second method that uses the first sealant member having through holes and the second sealant member closing the through holes, essentially discloses only description of cases in which the MEMS structure is manufactured separately. It gives no suggestion of the structure and the manufacturing process of the device in cases where a MEMS structure is fabricated integrally with an electronic circuit. Normally, it is difficult to enhance the structural integrity between a MEMS structure and an electronic circuit or to manufacture a MEMS structure in common processes with an electronic circuit, and it is necessary to manufacture a MEMS structure independently from the manufacturing process of an electronic circuit. Thus, the method not only keeps the manufacturing cost from being reduced, but also may adversely affect the performance of the MEMS structure as well as of the electronic element through technical impact that may be caused by the both processes.